1. Field of the Invention
The present invention relates to electron-emitting sources.
2. Description of the Related Art
An electron-emitting source that emits thermal electrons or field electrons is used as an electron beam source, discharge tube, or the like. In order to derive a large amount of high-energy electrons from low energy input, the electron-emitting source should be composed of materials that exhibit a low work function.
It has long been known that alkali metals, alkali earth metals, and the compounds thereof exhibit low work functions. These substances, however, have the disadvantage that they are very chemically active, and, for example, react with trace amounts of water in the atmosphere to change their characteristics. At present, LaB6 is put into practical use as a material for electron guns. LaB6 exhibits a work function of 2.66 to 3.55 eV, whose values must be further lowered in order to obtain higher performance. It is reported that when, for example, LaB6 is coated with BaO, an alkaline-earth metal oxide, the work function will be lowered into a range of 2.27 to 2.07 eV.